High temperature seal

ABSTRACT

A rubbing contact fluid seal, particularly suitable for use in a gas turbine engine rotary regenerator, comprising a reticulate metal facing layer bonded to a base member and adapted for rubbing contact with the regenerator, the facing layer having disposed in the pores thereof a seal material consisting of, by weight, 72 to 75 percent chromite powder and potassium silicate equivalent to 25 to 28 percent of an aqueous potassium silicate solution containing about 29.1 percent, by weight, potassium silicate which material is bonded in and to the facing layer by curing at 500* F.

nite States atent [151 3,666,001 Johnson 30, 1972 [54] HIGH TEMPERATURESEAL 3,102,038 8/1963 Fisher 106/302 Inventor: John N. Jo! Utica Mich3,130,061 4/1964 McMahon et al. ....l06/84 M [73] Assignee: GeneralMotors Corporation, Detroit, Primary Examiner-Robe" Smith iAttorney-Sidney Carter and Peter P. Kozak [22] Filed: Aug. 10, 1970 57ABSTRACT [21] PP 621257 A rubbing contact fluid seal, particularlysuitable for use in a gas turbine engine rotary regenerator, comprisinga reticulate 52 us. CL... ..277 234 277 234 metal facing layer bnded abase member and adapted 511 int. Cl ..F2 8d 19/00 rubbing with regeneramthe facing having 58 Field 01' Search ..277 234 81 96 117/169 A- dislmedthe Itores there a Seal material nsisting by 65/9 weight, 72 to 75percent chromite powder and potassium silicate equivalent to 25 to 28percent of an aqueous potassium 56] References Cited silicate solutioncontaining about 29.1 percent, by weight,

potassium silicate which material is bonded in and to the facing layerby curing at 500 F.

4 Claims, 5 Drawing Figures Patented May 30, 1972 2 Sheets-Sheet lINVENTUR. v civkn /7. (527mm AT ORNEV Patented May 30, 1972 2Sheets-Sheet 2 I NVENTOR. c/pkrz 2X e/zvimsoh B V HIGH TEMPERATURE SEALThis invention relates to an improved rubbing contact fluid sealsuitable for use in a rotary regenerator for gas turbine engineapplications and, more particularly, to an improved fluid seal materialfor such applications having a relatively low coefficient of friction,low wear rate, good chemical stability at elevated temperatures in anoxidizing environment and excellent resistance to sulfur-containingcompounds in the gas turbine engine exhaust gases.

Currently, there is a family of gas turbine engines which use rotatingdisc-type regenerators to recover usable heat from exhaust gases topreheat incoming combustion air. A necessary requirement of theregenerator system is an effective seal across the faces of the rotatingdisc to prevent leakage of the high pressure incoming air into thecounterflowing exhaust gas. A rubbing seal is desired as it has thepotential for lowest leakage. These rubbing seals are required tooperate at a maximum temperature of about 600 F. on the outboard or coldside of the seal and at temperatures up to 1,200 F. on the inboard orhot side of the seal. The desired properties of the rubbing sealmaterial are that it have good oxidation resistance and thermalstability, good wear resistance, a relatively low coefficient offriction over a wide range of temperatures, and that it exhibit overallcompatibility with the regenerator matrix material. In addition, sincemetallic regenerators assume a slight spheroidal inward bulge duringoperation, the seal must be flexible enough to conform to the shape ofthe regenerator.

In my copending application, Ser. No. 38,206 filed May 18, 1970 andassigned to the assignee of this invention, I described a particularlysuitable rotary regenerator rubbing contact fluid seal having theaforementioned desired properties comprising a reticulate metal facinglayer bonded to a base member and adapted for rubbing contact with theregenerator, the facing layer having disposed in the pores thereof aseal material consisting of, by weight, 53 to 67% NiFe Q, powder, 3 to18% ZnO and 28 to 32% aqueous sodium silicate solution which material isbonded in and to the facing layer by curing at 500 F. It has been found,however, that my improved seal material exhibits not only a relativelylow coefficient of friction, lowwear rate and good thermal stability atelevated temperatures in an oxidizing environment but also increasedresistance to attack by sulfur-containing compounds, particularly SO,and S in the gas turbine engine exhaust gases which results in longerseal life particularly at portions of the hot side of the seal which arecontinually exposed to engine exhaust gases.

Accordingly, it is an object of my invention to provide an improvedrubbing contact fluid seal for use in the regenerator portion of a gasturbine engine which has relatively low friction and wear properties,which is resistant to the deleterious effects of high temperaturestypical of those found in gas turbine engines, and which is resistant toattack by sulfur-containing compounds in the gas turbine engine exhaustgases.

In the preferred embodiment of my invention this object and others areaccomplished by providing a seal having a metallic base and a reticulatenickel facing layer adapted for rubbing contact with a rotatingregenerator matrix and characterized by'fibrils forming a substantiallyuniform, threedimensional skeletal network with interconnected porestherebetween bonded to the base with the seal being held against theregenerator matrix such that the facing layer is continuously in rubbingcontact with the opposed radial faces of the matrix. In accordance withthe principal feature of my invention the pores of the facing layer arefilled with a seal material consisting essentially of, by weight, about72 to 75 percent chromite powder and potassium silicate equivalent to 25to 28 percent of an aqueous potassium silicate solution containing about29.1 percent, by weight, potassium silicate which material is bonded tothe fibrils of the facing layer by a low temperature oven cure whereinthe potassium silicate binder forms a bond between the chromite powderand the facing fibrils.

As used herein, the term chromite refers to the naturally occurringminerals which are oxides of iron and chromium containing a majorportion of chromic oxides. The minerals are chromium-bearing spineltypes whose compositions can be expressed as (Mg, Fe")0 (Cr, AI, Fe OOther objects and advantages of my invention will become more apparentfrom the following detailed description of the invention reference beinghad to the accompanying drawings, of which:

FIG. 1 is a schematic sectional view of a rotary regenerator taken onthe plane indicated by line l-l in FIG. 2;

FIG. 2 is a sectional view of the same .taken in a plane indicated bythe line 2--2 in FIG. 1;

FIG. 3 is a sectional view of the same taken in a plane indicated by theline 3-3 in FIG. 1;

FIG. 4 is an enlarged view of a portion of the seal shown in FIG. 1; and

FIG. 4a is an enlarged view of a portion of FIG. 4.

FIGS. 1 to 3 generally show schematically a disc-type rotary regeneratorportion of a gas turbine engine (not shown). Referring first to FIG. 1,the regenerator comprises a housing 10 which is generally drum-shapedand which encloses an annular matrix 12 which is of a structure definingpores or passages 14 (greatly enlarged in FIG. 1) extending between theopposed radial faces 13a and 13b of the matrix generally parallel to theaxis of rotation defined by a driving shaft 16. The matrix 12 isfabricated from alternate spiral layers of flat and corrugated stainlesssteel sheet stock or a ceramic. Shaft 16 is mounted in suitable bearingsin a boss 18 on the housing and terminates in a spider 20 which iscoupled by means (not shown) to the matrix so that the matrix may berotated slowly. The matrix preferably includes a non-porous inner rim 22and a non-porous outer rim 24. A generally cylindrical space 26 isdefined within the interior of the matrix and a space 28 extends aroundthe periphery of the matrix within the housing 10. An inlet 30 for cold,high pressure air enters one face of the housing and opposite to it anoutlet 32 is provided for the heated compressed air. The hot, lowpressure exhaust gases enter through an inlet 34 and leave theregenerator through an outlet 36, the two streams thus being incounterflow relation.

A seal 38 is provided between each radial face of the matrix and thehousing in rubbing contact with the rotating matrix to confine the coldand hot gases to the desired paths through the matrix from inlet tooutlet and thereby minimize leakage between the paths. As shown moreclearly in FIGS. 2 and 3, such a seal comprises two arms 40 and 42extending radially of the matrix base preferably joined at the inner rimof the matrix by a circular seal portion 44 extending around theinterior cavity 26 and joined at the outer rim of the matrix by anarcuate rim or by-pass seal 46 extending around the high pressure pathand an arcuate rim seal 48 extending around the low pressure path. Theseal assembly thus defines an opening 50 for the cold, high pressure airand an opening 52 for the hot, low pressure exhaust gas. These openings,as shown in FIG. 2, conform generally in the outline of the ducts 30 and32, and 34 and 36, respectively.

The seal 38 in rubbing contact with the matrix 12 comprising portionsdefining the arms 40 and 42, the inner seal portion 44 and the outerseal portion comprised of arcs 46 and 48, as indicated in FIGS. 2 and 3,is comprised of a stationary base member 54 which is a flat sheet ofmetal, for example, a stainless steel sufficiently thick to bereasonably stiff and rigid,

'but sufliciently flexible to curve slightly in accordance with anydistortion of the matrix, and a facing layer 56 which covers the forwardor matrix face of the base 54, as shown in FIG. 3. During engineoperation, the seal is held against the accordance with the principalfeature of my invention the pores 62 of the facing 56 are filled with aseal material 64 which consists of chromite powder with a potassiumsilicate binder. This material performs with a moderate frictioncoefficient, low wear rate and exhibits good chemical stability at hightemperatures in an oxidizing environment which are necessaryrequirements for a seal material for use in a gas turbine engine rotaryregenerator. In addition, this material exhibits excellent resistance toattack by sulfur-containing exhaust gases. The seal material 64 fillsthe pores 62 of the facing layer 56 and is bonded to the fibrils 60 suchthat the facing retains and reinforces the chromite seal material andallows the seal to flex as the regenerator distorts in operation.

The porous facing may be any of the well-known cellular, reticular orsintered type structures having a porosity and pore configuration suchthat the chromite seal material forms a major part of the rubbingcontact surface while the facing acts only as a support structureforming a minor part of the rubbing contact surface. In this manner thefriction characteristics of the seal will be mainly those of thechromite material with the friction characteristics of the facing havingonly a minimal effect. It is also desirable that the facing be of amaterial having thermal expansion properties similar to the chromitematerial, the base 54 and the matrix 12 to minimize distortion orwarpage due to differing coefiicients of thermal expansion betweenmaterials. Nickel or nickel alloys containing predominately nickel havebeen found to be suitable materials for the facing. I have found that areticulate-type structure (shown schematically in FIG. 4a) which is athree-dimensional skeletal structure of interconnected fibrils with nomembranes or windows partitioning the contiguous pores, such as thatdescribed in an article appearing in the Apr. 1968 issue of MaterialsEngineering at page 44, to be a preferred facing structure because thereticulate structure allows the seal material to flow between theinterconnected pores and fonn a continuous seal phase. The structuredescribed in the article is a metal foam produced by electroplating alayer of nickel on a reticulated urethane substrate to produce acontinuous metal network of interconnected pores with a pore density of10 to I pores per inch. The Ball U.S. Pat. No. 3,1 11,396 discloses analternative method of forming the metal foam by depositing a slurry of aliquid and finely divided metal powder on an open-pore type organicstructure such as polyurethane and then sintering the coated structureto produce a continuous skeletal metal structure. I have found that areticulate nickel foam having a density of about 45 pores/inch serves asan excellent facing material.

The rubbing seal 38 for use in a rotary regenerator is formed by firstdisposing the porous facing layer about one-eighth inch thick on thebase 54 (FIGS. 3 and 4) and bonding the facing thereto such that thefacing conforms to and covers arms 40 and 42 and rims 44, 46 and 48. Inmy preferred seal construction, the base 54 is formed of type 430stainless steel and is about 0.060 inch thick. The members are bondedtogether by conventional powder furnace brazing. A suitable brazematerial is Nicrobraz 30 a product of Wall Colmonoy Corporation, whichhas a typical composition of 71 percent nickel, 19 percent chromium andpercent silicon.

The facing is filled by first preparing a slurry composition consistingof from about 72 to 75 wt% of chromite powder and from about 25 to 28wt% aqueous potassium silicate solution. A suitable type of aqueouspotassium silicate solution is Kasil No. 1, a product of thePhiladelphia Quartz Company which, as shown below, contains about 29.1percent, by weight, potassium silicate and which has the followingproperties as listed by the manufacturer:

Weight ratio SiO /K O 2.50 Weight SiO 20.8 Weight K 0 8.30 Density, Bc29.8 Density, lbs/gal 10.5 Viscosity, centipoises 40 The slurrycomposition is placed in a vertically positioned tube having an openingsurrounded by an annular disc placed tightly against the facing. Pulsesof air are applied to the slurry by means of a solenoid valvearrangement whereby the slurry flows out the opening and into thesupport. The base seals the bottom side of the facing while the annulardisc seals the top thereby causing the slurry to flow concentricallyoutward filling the pores of the facing.

After filling, the seal is subjected to an oven curing treatment toremove the water from the slurry and to bond the chromite powder to thefacing fibrils, as previously mentioned. The curing treatment used is asfollows:

Heat to 150 F., hold for 2 hours Heat to 175 F., hold for 1 hour Heat to200 F., hold for 1 hour Heat to 225 F., hold for 1 hour Heat to 250 F.,hold for 1 hour Heat to 500 F., hold for 1 hour All heating rates above150 are at 50 F. per hour The curing treatment is performed in astep-like manner in order to avoid bubbling of the potassium silicate.

For the purpose of demonstrating the utility of my invention, l-inchdiameter test buttons were made and held in a stationary fixture againsta rotating regenerator-like disc having a construction similar to thatof a full size regenerator. The following test parameters were used:

Disc material type 430 stainless steel Disc braze material The resultsof the test are as follows:

Disc wear 0.1 mils Seal wear 0.3 mils Sliding Friction Coefficient0.2-0.25 Percent contact Disc damage none Control samples which wereplaced in an oxidizing environment at 1,200 F. for the 5.5 hours showedan average amount of oxidation of 0.5 mils.

For the purpose of demonstrating the life of my seal material, longrange testing was performed at l,200 F. using the same parameters as inthe aforementioned test but at a sliding speed of 84.4 feet/min. for1,000 hours. Examination of the seal and disc after testing showednegligible seal wear, an average disc wear of 0.6 mils and a sealcontact area of over percent. No damage was noted to the disc. Controlsamples which were placed in an oxidizing environment at 1,200 F. forthe 1,000 hours showed an average amount of oxidation of 0.3 mils.

In addition to the wear and life tests previously described, corrosiontests were performed to determine the resistance of my seal material toattack by sulfur-containing compounds typically found in gas turbineengine exhaust gases. In these tests the seal test buttons were exposedto an air 1 percent S0 atmosphere for hours at 1,200 F. and showed nodeterioration as a result thereof. Similarly, in engine durability testsno seal deterioration was seen after 300 400 hours of service.

From the foregoing, it will be noted that my seal material is arelatively low-friction, low-wear material which is resistant tooxidation and deterioration at elevated temperatures and which isresistant to attack by sulfur-containing compounds in gas turbine engineexhaust gases. Although my invention has been described in terms ofpreferred embodiments with reference to a particular rotary regeneratorstructure, it will be appreciated that other forms may be adopted withinthe scope of my invention. For example, in many regenerator operationsthe outboard or cold side of the seal and the rim of the hot side sealoperate at less than 800 F. In this case my seal material may bereplaced in these regions with graphite, which has a coefficient offriction of about 0.05 but which oxidizes above 800 F., with my sealmaterial being used only on seal regions which operate at temperaturesup to 1,200 F.

Thus having described my invention what is claimed is:

1. A rubbing contact fluid sealing member comprising a base member and aporous layer formed of a metal having temperature resistance andoxidation and sulfidation resistance at temperatures in excess of 1,200P. adapted for rubbing contact bonded to at least a portion of said basemember with a seal material filling the pores of said layer and bondedtherein, said layer having a pore density in the range of about to 100pores/inch, said seal material being formed and bonded to said layer byheating a composition consisting essentially of, by weight, about 72 to75 percent chromite powder and potassium silicate equivalent to 25 to 28percent of an aqueous potassium silicate solution containing about 29.1percent, by weight, potassium silicate for a time and at a temperatureof at least about 500 F. to substantially completely cure said potassiumsilicate solution in said pores.

2. A fluid sealing member as defined in claim 1 wherein said layer isreticulate nickel foam having a pore density of about 30 to 60pores/inch.

3. A fluid seal for use in the rotary regenerator portion of a gasturbine engine, said portion including a housing adapted to enclose arotating regenerator matrix, said seal comprising, in combination, astationary metal base and a reticulate layer formed of a metal havingtemperature resistance and oxidation and sulfidation resistance attemperatures in excess of l,200 F. characterized by fibrils forming athree-dimensional skeletal network with interconnected porestherebetween bonded to at least a portion of said base, and means forretaining said base member between said housing and said matrix withsaid layer being adapted for rubbing contact with said rotatingregenerator matrix, said layer having a pore density in the range ofabout 10 to pores/inch, the pores of said layer being filled with a sealmaterial bonded therein, said seal material being formed and bonded insaid layer by heating a composition consisting essentially of, byweight, 72 to 75 percent chromite powder and potassium silicateequivalent to 25 to 28 percent of an aqueous potassium silicate solutioncontaining about 29.1 percent, by weight, potassium silicate for a timeand at a temperature of at least about 500 F. to substantiallycompletely cure said potassium silicate solution in said pores.

4. A fluid sea] as defined in claim 3 wherein said layer has a poredensity of about 45 pores/inch.

2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 300 Dated May 30, 1972 Inventonis) John N. Johnson It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2,- line 3, "(Mg,Fe )O- (Cr,Al,Fe 0

should read (Mg,Fe )0' (Cr,Al,Fe O

Signed and sealed this 10th day of October 1972.

(SEAL) Attest:

EDWARD M.FLEICHER,JR. ROBERT GOTTSCHALK Commissioner of PatentsAttesting Officer

2. A fluid sealing member as defined in claim 1 wherein said layer isreticulate nickel foam having a pore density of about 30 to 60pores/inch.
 3. A fluid seal for use in the rotary regenerator portion ofa gas turbine engine, said portion including a housing adapted toenclose a Rotating regenerator matrix, said seal comprising, incombination, a stationary metal base and a reticulate layer formed of ametal having temperature resistance and oxidation and sulfidationresistance at temperatures in excess of 1,200* F. characterized byfibrils forming a three-dimensional skeletal network with interconnectedpores therebetween bonded to at least a portion of said base, and meansfor retaining said base member between said housing and said matrix withsaid layer being adapted for rubbing contact with said rotatingregenerator matrix, said layer having a pore density in the range ofabout 10 to 100 pores/inch, the pores of said layer being filled with aseal material bonded therein, said seal material being formed and bondedin said layer by heating a composition consisting essentially of, byweight, 72 to 75 percent chromite powder and potassium silicateequivalent to 25 to 28 percent of an aqueous potassium silicate solutioncontaining about 29.1 percent, by weight, potassium silicate for a timeand at a temperature of at least about 500* F. to substantiallycompletely cure said potassium silicate solution in said pores.
 4. Afluid seal as defined in claim 3 wherein said layer has a pore densityof about 45 pores/inch.